Husqvarna 40 Rancher - What am I overlooking

[Blade]

Presently feeling like the Forest Gump of chainsaw repairers....

Customer brought in a mint condition 1986 Husqvarna 40 Rancher chainsaw, albeit with a minor piston scoring caused by bad fuel mix. Simple enough job, and an hour & half later the saw was running like new after a new piston & carburettor rebuild, then test run and set idle to 2500 rpm (factory specs)........well almost running as new!

Placed the bar & chain back on to do the final tune, however the chain is now constantly running. Did the usual tinkering checks and adjustments, and even consulted the OEM workshop manual. I'll be honest and say I maybe see one of these models perhaps once or twice a year, so don't profess to be an expert on these models.

Clearly there is something very minor I've overlook here.....any suggestions on what 'Forest' is missing here?

 

[Whiskers]

Could be a bad clutch or a missing clutch spring. I've also seen things bind up the drum before. If it was put together wrong the retaining clip might be binding the drum to the crank.

 

[Blade]

Could be a bad clutch or a missing clutch spring. I've also seen things bind up the drum before. If it was put together wrong the retaining clip might be binding the drum to the crank.

Thanks for the reply it's appreciated.

The spring is in place, but I'm starting to think it may be a bad clutch, despite the fact it looks almost new. About to pull it down again tomorrow when I'm back in the workshop for a closer look.

 

[Rockjock]

If you have the idle set to factory specs then I too would look at the clutch. Broken or weak spring can be the issue

 

[ANewSawyer]

No air leak, right? I saw an engine that had an air leek that I couldn't stop the chain on and it turned out that the primer bulb was broken. The engine was leaning out by pulling air through the broken primer bulb.

 

[calebng15]

Might be your needle bearing is froze up. Try spraying it with a little PB blast. Might be your only problem. I've bought clutch springs before, and it ended up being the bearing!

 

[fearofpavement]

Could it be the wrong clutch? A missing washer? An extra washer? Dry clutch bearing?
Have you tried slowing the engine down more?
Another thing to check, when you pull the starter rope, does the chain move or only when running? If it moves the chain when pulling the starter, then there is some type of issue other than weak clutch springs.

 

[Rockjock]

Had an 038 in yesterday exact same symptoms, 1 broken clutch spring. Easy fix.

 

[Chainsaw Jim]

It's it a Stihl sprocket? I think an 031 sprocket will fit those, but it makes it a direct drive with no working clutch.
If the springs are weak or broken then you should be able to tell be prying on them with a flat head screwdriver to check tension.

 

[Blade]

Thanks for all the assistance guys it was greatly appreciated. After a suggestion from fearofpavement, it turned out the spur sprocket kit supplied had the correct part number, but for the later series Model 40, as opposed to the early series saw I was working on.

There was a minor difference of only about 1mm in the depth, and it was this that was causing the spur sprocket to lock up on the spacing washer.

Thanks again for the replies.

 

[Whiskers]

Nothing like a nice cheap fix!